Testing appliance for multiple-switchboards.



Patented Dec. 3|, l90l.

J. L. MGGUARRIE.

TESTING APPLIANCE FOR MULTIPLE SWITGHBOARDS.

(Application filed Mar. 22, 1897.)

(No Model.)

5 Wm TR MM Y M L S F. M J

ATTORNE X m: uoams pzrzns co, wow-mum WASH'NGTON. n. c.

Units STATES PATENT OFFICE;

JAMES L. MCQUARRIE, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE \VEST- ERNELECTRIC COMPANY, OF ILLINOIS.

OF CHICAGO, ILLINOIS, A CORPORATION TESTING APPLIANCE FORMULTIPLE--SWITCHBOARDS.

SPECIFICATION forming part of Letters Patent No. 689,903, dated December31, 1901 Application filed March 22, 1897. Serial No. 628,685. (Nomodel.)

To all whom it 72mg concern:

Be it known that 1, JAMES L. MCQUARRIE, a citizen of the United States,residing at Chicago, in the county of Cook and State of Illinois, haveinvented a certain new and useful Improvement in Testing Appliances forMultiple Switchboards, (Case No. 3,) of which the following is a full,clear, concise, and exact description, reference being had to theaccompanying drawing, formingapart ofthisspecification.

My invention concerns means for testing a line at one section of amultiple switchboard to determine whether it be already in use at someother section of the switchboard. It applies particularly toswitchboards equipped with automatic signals associated with the linesand with a central source of current permanently connected with thelines to operate the signals, and it is designed to obvi ate certainconditions which give rise to false test-signals in such switchboards.In the type of telephone switchboard mentioned each line is providedwith a test-ring whose electrical condition becomes changed whenconnection is made with the line in the switchboard, and theconnecting-plugs and their plug-circuit are provided with supervisorysignals controlled by magnets interposed in the plug-circuit andresponsive to currents through the lines determined by the use of thetelephones at the substations, together with a source of current in abridge of the plugcircuit intermediate of the signal-controlling magnetsand an impedance-coil in the bridge with the source of current. In asystem of this type a false test-signal will be produced when a test ismade in the usual way with a plug whose mate has been employed inanswering the call on account of current from the central sourcereturning through the circuit of the calling-line and changing theelectrical condition of the testing-plug.

My invention aims to avoid this condition; and it consists inswitch-contacts associated with the operators listening-key constructedto break the continuity of the plug-circuit during the act of testing,leaving the tip of the testing plug withoutimmediate electricalconnection with the remainder of the plugcircuit, so that it shall notbe altected by changes in the condition of the plug-circuit.

In a form of my invention suitable for practical employment theimpedance-coil before mentioned is divided into two helices, which areplaced in inductive relation to each other after the manner of arepeating-coil and which are connected together and to earth at onepoint. The switch-contacts upon thelistening-key are arranged to unitethe other extremities of the two windings while the telephone isdisconnected from the circuit, leaving them separated and in position toexercise their function as a repeating-coil while the telephone is inuse. The parts are arranged in duplicate for use in metallic circuits.

The invention is shown in the attached drawingin connection with theswitching system before described. Therein two substations arerepresented connected by line-circuits with switching and signalingappliances in a switchboard. The latter is shown equipped with a singlepair of connectingplugs and their plug-circuit, with the usual accessoryappliances, and with the circuits and mechanism for testing whichconstitute my present invention.

The apparatus at the substation may comprise a transmitting-telephone aand a receiving-telephone a, a polarized signal-bell a a condenser a anda switch a The bell a and the condenser a may be connected in apermanently-closed bridge 1 of the line-circuit 2 3, the telephonesbeing included in a bridge 4, which is closed through the action of thetelephone-switch when relieved from the weight of the telephone. At thecentral office the line conductors 2 3 are connected with spring-jacksZ) and b in two different sections of a multiple switchboard. Conductor2 is led directly to earth, while conductor,

3 is connected with the relay 0, and thence through a battery d toearth. luterposed in the extensions of each of these conductors 2 and 3is a pair of normally-closed switch-contacts of a second relay 6. Thelatter when excited breaks the connection of the one line conductor withthe earth and of the other with the relay and battery. Theswitch-contacts of the relay 0 control a local circuit 5, which includesa subsidiary signal-lam p f,associated with the spring-jack b in one ofthe switchboards, together with a source of current suitable forilluminating the lamp. The relay 6 is included in a portion 6 of asecond local circuit,which becomes closed, as will be hereinafterdescribed, when a connection is made with the line.

The apparatus of the two lines is of course alike. The signal-lampsfandthe answerin g-jacks with which they are associated may be assumed to belocated upon different sections of the switchboard, however, so thatcalls from the difierent lines are answered by difierent operators.

The plugs g and g are of usual construction,each having three contactportions ad apted to make connection with the two line-confacts It and hand the local contact or testring 72 of the spring-jacks. The likelinecontacts of the two plugs are normally united through conductors 7and 8, which constitute the plug-circuit. The usual calling-key e' isinterposed in these conductors, constructed to loop a generator ofsignaling-current into circuit with plug g, and a listening-key 7c isprovided for bringing the operators telephone [into a bridge of theplug-circuit. A permanently-closed bridge 10 of the plug-circuitincludes the common source of current d for actuating the signals of theline, together with the windings of an impedance-coil n. One pair ofwindings n n of this coil are interposed in parallel in conductor 10between the battery d and the conductor 8 of the plugcircuit. Two otherwindings n and n" are interposed in the same bridge conductor, be tweenthe source of current and the strand 7 of the plug-circuit. Theterminals of the windings n and n are connected together during thenormal use of the plug-circuits through the agency of anauxiliary-switch contact of the listening-key 7a, which becomes closedto the switch-spring of the key when the key is in position to interruptthe connection of the operators telephone with the plug-circuit. Theother windings n n are similarly brought into multiple through theagency of another anvil 7c in the key. Thus while the operatorstelephone is not in connection with the plug-circuit the conductors 7and 8 of the plug-circuit are practically continuous. While the key isin position for the use of the telephone, however, the circuit ofconductor 7 is from the tip of plugg through coil 01 to ground and fromthe tip of plug g through coil 02 to ground. The circuits from thering-contacts of plugs g and g are through the helices n andairespectively, to the free pole of battery d. Hence while the telephoneis in use the tip of the testing-plug g, being grounded through winding71, is free from disturbance by the the terminals of conductors 11 and12, re-

spect-ively, which are led to the free pole of a grounded source ofcurrent 19. These conductors include supervisory signal-lamps q and g,which are associated, respectively, with plugs g and g, each of which iscontrolled through the agency of a shunt including the contact-pointsofthe corresponding relay 0 and 0'. The battery 13 thus serves when a plugis inserted into the spring-jack to ex cite the cut-off relay e of thecorresponding line to electrify the test-rings h of that line to producethetest and to illuminate either of the supervisory lamps q or q whoseshunt may be interrupted in its controlling-relay.

The operation in general of the system is, briefly, as follows; Theremoval of the receiving-telephone from its switch-hook at thesubstation closes the line-circuit at the station and causes theexcitement of the relay 0, whereby the circuit 5 becomes closed and thecorresponding linelampf is lighted. Responding to the signal,theoperator inserts an answering-plug 9 into the answering-jack b of theline, at the same time placing her listoning-key 7c in position to bringher telephone into connection with the plug-circuit. The act ofinserting the pluginto the springjack causes the cut-off relaye to breakthe normal ground connections of the line, and thus to render relay 0inert and to extinguish the'line-signalf. The same actchanges theelectrical condition of test-rings h 'of the line, so that they shalltest busy subsequently. The supervisory lamp q does not become lighted,because of the current from source (1 through relay 0 to the substation,which causes the relay to close the shunt about the supervisory lamp.Having learned the order for the correspondin line, the operator touchesthe tip of plug 9 to a test-ring h of the required line. If noconnection exists with the line tested, the test-contacts h of thespring-jacks b and b are merely connected to earth and become a part ofa circuit leading from earth through the testcontact, the tip of theplug g, a portion of conductor 7 of the plug-circuit, the winding n ofthe impedance-coil, and a portion of conductor 10 to earth, and sincethis circuit includes no source of current no electrical change takesplace in the circuit whenclosed. If, however, a connection alreadyexistswith the line, the battery 19 is connected with the test-contactsby wayof conductor IIO 12 andthe sleeve-contact of a plug'g,by means of whichconnection has been made, whereby the potential of the test-contacts ofthe line is raised above that of the earth, so that a current will thenflow through the tip of the test-plug at each application of thetest-ring, which, acting inductively upon the winding of, will produce acurrent in the circuit made up of a portion of the bridge 10, winding aa portion of the conductor 7, the operators telephone-bridge, a portionof conductor 8, and winding 91', which will cause a click in theoperators telephone.

In the early stages of the development of the central-batteryrelay-switchboard it was customary to supply battery to theconnecting-cord circuit througha bridged retardation orimpedancecoil.Vithacircuitsoarranged, however, trouble was experienced on account of afalse busy test which was obtained when an operator undertook to testwhile the answering-plug of her pair of connecting-cords was inserted inthe jack of a metallic-circuit line. The cause of this difficulty lay inthe current which, flowing out over one side of the metallic circuitthrough the bridge at the substation and returning over the other sideof the circuit, raised the potential at the tip of the calling-plugsufficiently to causeabusy click in the operators telephone. Wheneverthe tip of the calling-plug was touched to the test-ring of a jack,whether the line associated with that jack were busy or not, a currentwould find path back to the grounded side of the battery, through thegrounded connection of the busy-test ring, as well as through theconnection from the tip side of the plug-circuit to the grounded side ofthe battery through the impedance-coil, enough current being diverted tothe test-ring to pro duce the click. By the use of my invention it isobvious that such a false test-signal is avoided, because when the keyis depressed for testing the direct connection between the tips of thetwo plugs is broken, and current returning from the calling-station byway of the tip of the answering-plug would not find path to the tip ofthe test-plug, since the grounded pole of the battery is connectedbetween the windings n or, and the normal short circuit of said windingsis broken.

Having tested the line and found it free for use, the operatordisconnects her telephone by means of the listening-key 7t and insertsthe plug g into the spring-jack of the line called for. The change ofposition of key 7t necessary to disconnect the telephone incidentallycloses the switch-springs of the key upon the contacts L 15respectively, and thus unites the severed portions of conductor 7 and ofconductor 8, leaving the bridge 10 complete and including a pair ofwindings in multiple at each side of battery (Z.

The connection of plug g with the line called for effects the cuttingoff of the linerelay 0 of that line and changes the condition of thetestrings to make the line test busy. Until the response of the calledsubscriber no current flows through relay o. Hence the supervisory lampq, being as yet not shunted, remains lighted. The response of the calledsubscriber is indicated to the operator by the extinction of this lamp.

The replacement of the telephones at both stations causes the lightingof both supervisory lamps q and g, which may be taken as signifying thediscontinuance of conversation.

I claim as my invention- 1. The combination with a plug and aplugcircuit, said plug having a contact adapted for testing lines todetermine the electrical condition thereof connected through a helixwith earth, of a key adapted to disconnect the said test-contact fromits normal connection with the remainder of the plug-circuit andsimultaneously to bring the operators telephone into connection with awinding in inductive relation to the said helix, substantially asdescribed.

2. The combination with a pair of plugs and the plug-circuit thereof, acontact-piece of one of the plugs being adapted to test the electricalcondition of lines, of a bridge of the plug-circuit, and a source ofcurrent included therein, an impedance-coil with two windings betweensaid source of current and the conductor of the plug-circuit terminatingin said test-contact, said windings being connected in multiple, anoperators listeningkey for connecting a telephone with the plugcircuit,and switch-contacts of the said key adapted to break the multipleconnection between the said two windings and thereby to interrupt thenormal connections of the plugcircuit, substantially as described.

3. The combination with a metallic-circuit telephone-line closed at thesubstation, and extensions of the line conductors terminating in thecontact-pieces of a connecting-plug, one of said contact-pieces beingadapted for testing the electrical condition of lines, of two helices ininductive relation interposed serially in the conductor leading to thetestcontact, a bridge of the line connected with the point of junctionof the helices, said point of junction being grounded, a key-adapted toconnect the said helices in multiple, and a test-indicating appliance inassociation with the conductor terminating in the test-contact torespond to currents therein; wherebyinterference with the test bycurrent in the line-circuit is prevented, substantially as described.

4. The combination with a metallic-circuit telephone-line and a doubleplug having its contact-pieces connected with the line conductors, onecontact-piece of the plug being adapted for use in testing, and anoperators listening-key, of a bridge of the line including a source ofcurrent, said bridge being current which is connected with thetest-condivided into multiple branches, a Winding of tact, as described.10 an impedance-coil in each of the branches, In Witness WhereofIhereunto subscribe my switch-contacts in the listening-key adapted namethis 21st day of November, A. D. 1896.

to break or close each conductor of the line- JAMES L. MCQUARRIE.circuit between the points of connection of Vitnesscs:

the said branches therewith, and a ground ELLA EDLER,

DUNCAN E. WILLETT.

connection from that portion of the source of

